Doped Keggin Heteropolyacids as Catalyst in the Solvent-free, Multicomponent Synthesis of Substituted 3,4-dihydropyrimidin-2-(1H)-ones

We report the use of V, Bi and Bi-V Keggin structure where Mo is partially replaced by V, Bi, and Bi and V, respectively, in the solvent-free multicomponent synthesis of 3,4-dihydropyrimidin-2-(1H)-ones by the Biginelli method. The incorporation of V, Bi and Bi-V in the structure of PMo notably increases the catalytic activity. The following correlation between the yields of the 3,4-dihydropyrimidin-2-(1H)-ones and the number of acidic sites of the catalysts was observed: PMoBiV > PMoV > PMoBi > PMo. The reaction experiments were performed in the absence of solvent, at 80 degrees C (1 h). Under these conditions and using the most active catalyst (PMoBiV), twelve examples were obtained with very good yields (80%-98%) and high selectivity. The catalyst was easily recycled and reused without appreciable loss of its catalytic activity. The synthetic method presented is a simple, clean and environmentally friendly alternative for the obtention of substituted 3,4-dihydropyrimidin-2-(1H)-ones.